Application of sensors in smart wearable devices

The lesser-known sensors in wearable devices

Galvanic Skin Sensor

I believe every reader has had this experience: before you start a very important task, you will feel nervous and anxious, and your hands and feet will sweat. This psychological reaction is transformed into a physiological reaction, which can be detected by the skin electrical sensor.

Sensoree's mood sweater uses galvanic skin response to sense people's moods and uses different colors of lights to express them.

Galvanic skin sensors are an important part of polygraphs

The polygraph works with a combination of galvanic skin sensors, a respiration rate sensor, and a heart rate sensor.

It should be noted that the skin galvanic sensor cannot test the user's emotions, but can only sense whether the user's psychological state has changed. Through this change, we can draw some conclusions. For example, the skin galvanic sensor of a lie detector can sense the psychological changes of the subject when speaking, and thus determine whether he is lying.

For example, studies have shown that when people are engaged in a day's activities, the level of skin electrical response is lower when they just wake up in the morning and go to bed at night, while the level of skin electrical response is relatively high during a certain period in the morning and afternoon, and this period is when we are most efficient in studying or working.

If we use the skin electrical sensor to detect the level of our human skin electrical response over a few days, we can know which time of the day our work efficiency is highest through the height of the skin electrical waveform.

For skin electrical sensors, we must understand:

1. The human skin's electrical response is affected by three factors: temperature, human activity, and psychological reaction. The skin's electrical sensor will therefore be affected, and its accuracy needs to be tested.

2. People have many emotions in a day, and the time and category of emotions are different every day. Even if we can accurately measure the galvanic skin response, classifying and organizing these data and giving scientific advice are still the biggest headaches for manufacturers.

Heart rate sensor

As a super weapon of personal health equipment, heart rate sensors can track exercise intensity, different sports training modes, etc. by monitoring heart rate, and can infer health action data related to it, such as sleep cycle, based on this data.

Diagram showing the relationship between heart rate changes during sleep and sleep status

Since the pulse rate changes with the sleep cycle and decreases when sleep deepens, we can monitor sleep quality by the changes in heart rate during sleep. However, due to the low accuracy of heart rate sensors on mobile devices, the reliability needs to be considered. It is said that in order to ensure the reliability of heart rate measurement, Apple Watch has designed four heart rate sensors to accurately measure heart rate.

At present, the electrode heart rate sensor is commonly used in hospitals, which has higher accuracy.

There are currently two types of heart rate sensors, one is a photoelectric heart rate sensor that measures by light reflection, and the other is an electrode heart rate sensor that measures the electric potential of different parts of the human body. Although the former has poor measurement accuracy, its advantage is its small size, so all mobile terminals currently use this method for measurement. We often see the latter when measuring electrocardiograms in hospitals. This method measures the changes in electric potential at different points on the human body to measure changes in heart rate. This method is accurate, but it must monitor two parts of the human body at the same time. When we usually use mobile phones and watches, we touch the products with one hand, so continuous monitoring is not possible.

What we must understand about heart rate sensors:

1. Simply giving a heart rate value does not mean much to you. If you can measure it continuously and give health advice such as sleep quality/rest time based on the heart rate data over a period of time, it will be of great help to users.

2. Currently, most mobile terminals use photoelectric heart rate sensors, which have a higher probability of error than electrode heart rate sensors.

3. Electrode heart rate sensors cannot be used on smaller wearable devices at present, but some manufacturers are working on it. I believe they will become a signature accessory for high-end devices in the future.

Barometer

The barometer is a little thing that is often hidden but very useful. Although it can only measure air pressure data, we can use this data to accurately know the altitude of the machine. If we monitor the changes in air pressure over a period of time, we can also obtain the data on the change in machine altitude, thus preparing for further data processing.

With a barometer, you can know the altitude and you don't have to worry about not being able to navigate on such a double-decker road.

Sports watches are equipped with barometers to provide athletes with altitude data

So what benefits can the barometer bring to users through the altitude data it measures? Outdoor athletes can intuitively understand their altitude; future navigation maps can not only know our plane position, but also know our floor, which is definitely an inevitable trend in the development of future navigation; wearable devices can only detect the number of steps people take every day, but a barometer can also detect the number of stairs walked, making the calorie consumption data more accurate.

Things we must understand about barometers:

1. Since it is a component that measures air pressure, abnormal changes in air pressure will inevitably affect the effectiveness of the information obtained by the user. For example, when an airplane is flying, the cabin will be pressurized for the comfort of passengers. At this time, the air pressure value inside the airplane is different from that outside, so we cannot get the correct altitude information.

2. Currently, barometers are widely used in mobile terminals, but due to the lack of application software support, they are often ignored by users.

3. The barometer is a very practical component. We can use the equipment equipped with it to read the altitude information when climbing.

Summarize

The emergence of wearable smart devices has brought us a new lifestyle, but due to the limitations of technology level, cost level and other factors, wearable smart devices are not mature enough and cannot meet satisfactory expectations. However, as a very important part of sensors, especially the various functions of wearable smart devices, they all rely on the functional integration and innovation of various sensors to achieve. Therefore, it is necessary to develop more accurate, miniaturized and integrated sensors to meet the needs.

In the future, with the continuous advancement of modern "electronics-sensor" technology, wearable devices will continue to develop as always. During this period, various new sensors will emerge in an endless stream, and the application of sensors will enter a more brilliant future.